The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Rotating storage systems such as magnetic disk drives and optical disc drives utilize servo control techniques based on back electromotive force (BEMF) of a voice coil motor (VCM) or data recorded on a rotating storage medium. The information is used to control movement of a head over the rotating storage medium from a current track position to a target track position during seek operations. A parking area or ramp portion for the head may be provided outside the storage medium. The head is parked on the ramp portion when not in use. In addition, the rotating storage system may include latch mechanisms that secure the head from impact when parked in the ramp portion.
The latch mechanisms typically include a magnetic latch and/or an inertia latch. The magnetic latch generally prevents the head from falling onto the storage medium due to a relatively mild impact. The magnetic latch is usually composed of a magnetic material and a magnet, in which the magnetic material is arranged on a section of an arm (e.g., the coil section of a voice coil motor (VCM)) to which the head is attached and the magnet is arranged on a housing of the storage system. Attraction between the magnetic material and the magnet opposes movement of the arm.
The inertia latch generally prevents the head from falling onto the storage medium due to a strong impact. The inertia latch is usually composed of an inertia arm having two claws—a first claw is typically arranged on the housing of the storage system and a second (opposing) claw is typically arranged on a section of the arm to which the head is attached. During an impact, the first claw moves with the inertia of impact and engages the second (opposing) claw to oppose movement of the arm.
During operation of a storage device, burst data is generally used to detect the position of the head over the storage medium. However, during load control, burst data typically cannot be read. Load control refers to the movement of the head from a parked position in the ramp portion to a position over the storage medium. During load control, burst data cannot be read. Burst data is used to detect the position of the head over the storage medium. Therefore, the load control employs speed control. Also, positioning control may be performed by using the BEMF of the VCM.
When the head is loaded (or removed from a parked position on a ramp), external forces may act on the arm. The external forces can include a frictional force between a head supporting member and the ramp, an elastic reaction force of a wiring member, and/or friction around an axis of rotation of the storage medium. Additionally, when the rotating storage system includes the ramp portion and the latch mechanism, the external forces may include an attractive force of the magnet and/or a frictional force between the claw of the inertia arm and the opposing claw. As the external forces increase, higher driving current is required to overcome the external forces. This, in turn, increases the variation in the head moving speed during feedback control. As a result, the head moving speed takes longer to attain a target value.